This invention relates to polyimide copolymers prepared by the reaction of a mixture of dianhydrides reacting with a diamine. More specifically, it relates to polyimide copolymers prepared from a mixture of 4,4'-oxydiphthalic dianhydride (ODPA) and 3,4,3',4'-biphenyltetracarboxylic dianhydride (BPDA) and either 4,4'-oxydianiline (ODA) or p-phenylenediamine.
Dianhydrides, such as ODPA, may be reacted with diamines to form polyimide resins. The formation of the polymer is a two step process. In the first step, the dianhydride reacts with the diamine to form a polyamic acid which generally remains in solution. The polyamic acid solution is then subjected to a curing process which includes heat. The solvent evaporates, and the polyamic acid releases water to form the final polyimide. Chemical methods of curing are also available.
There are several methods for forming objects from polyimides. For example, the polyamic acid solution may be spread on a surface and cured to form a film. The surface need not be flat. Alternatively, the polyamic acid solution may be cured to form the polyimide which may then be subjected to heat and pressure to form objects.
Polyimides were first prepared by T. M. Bogert, et al, J. Am. Chem. Soc. (1908) 30, 1140. U.S. Pat. No. 2,710,853 discloses polyimides based upon pyromellitic acid. Polyimides based upon BPDA are disclosed in U.S. Pat. No. 4,247,443. The use of both BPDA and ODA in the preparation of polyimide polymers is disclosed in U.S. Pat. No. 4,290,936. Tim Tanunina, et al [Plast. Massy (9) 45-7, 1975 (in Russian)], describe polyimide copolymers prepared from 4,4'-diaminodiphenylether (ODA) and pairs of the following dianhydrides, pyromellitic dianhydrides (I);
3,3,4,4'-tetracarboxydiphenyl oxide (II); 3,3',4,4'-benzophenone tetracarboxylic acid (III); and 3,3',4,4'-diphenylsulfide tetracarboxylic acid (IV). The pairs of dianhydrides studied were II and III, I and II, and III and IV. The article discusses the glass transition temperature and densities of the copolymers formed, and compares them to the characteristics of homopolyimides.
Japanese Patent number SHO 63 [1988]-264121 discloses gas separation membranes prepared from polyimide polymers. The polyimides in question are copolymers containing ODPA and BPDA coupled with a variety of diamines including ODA and para-phenylenediamine.
Polyimides are used for wire insulation in certain specialized applications such as aircraft and spacecraft. Polyimides are also used in tape automated bonding (TAB) of semiconductor devices. In TAB semiconductor packaging, a thin sheet of copper is bonded to a polyimide film. The copper is etched to form leads and the semiconductor is then attached to the polyimide film. The leads on the TAB film may then be attached to the semiconductor. The TAB technology allows each chip to have a greater number of leads, and to be connected to the circuit board without having to drill holes through the board. In addition, TAB chips require less vertical space than conventional chips, and therefore, allow more compact circuitry. U.S. Pat. No. 4,063,993 discloses specific methods for bonding semiconductor leads to a tape and also discloses the use of polyimides as the basis of such a tape.